1. Field of the Invention
The present invention relates generally to instruments for measuring the concentration of a gas in a fluid and more particularly relates to an improved sensor including a sensor capsule for facilitating positioning an analyte sensitive element at the end of an optical fiber probe.
2. Description of Related Art
Various forms of analyte measuring instruments have been designed and developed for use in numerous medical and industrial applications. Among these devices are those that rely on optical properties of a sensing element containing a dye which is responsive to a particular analyte. When the dye interacts with the analyte the dye undergoes an optical change, such as a change of fluorescence, which is measurable and is directly related to the concentration of the analyte contained in the medium being sampled.
The analyte sensitive substance or indicator is located in a sensor element typically including a permeable membrane allowing the analyte to permeate and interact with the indicator. The indicator, typically a dye solution. has in prior devices been held trapped between the permeable membrane and an optical sensing surface, for example. the end of a probe, and has required a dye retaining mesh. A recognized need in the use of these sensors is the ability to interchange the element containing the indicator. It is desirable to change the element containing the indicator for various reasons. including to avoid transfer of contamination when the sensor probe is applied to different sensing locations, or due to the dye leaching out of the sensor. or for other reasons which make it desirable to interchange sensor elements.
The present invention provides a sensor capsule for use in combination with a fiber optic sensor. In particular, the present invention is specifically designed for use in a carbon dioxide sensor.
The sensor capsule comprises a two-piece snap together cap including an outer housing portion and an inner insert portion which fits within the housing portion. The housing and insert portions cooperate to retain a perforated metal disc. a sensor membrane, a covering membrane and a sandwiched dye layer at a predetermined position within the sensor capsule.
The sensor membrane comprises a silicone membrane positioned in engagement with the perforated metal disc and includes an indentation defining a dye well containing an indicator dye solution. The covering membrane comprises a TEFLON (polytetrafluoroethylene) membrane positioned over the silicone membrane to retain the dye solution within the dye well.
The snap together design of the sensor capsule assembly holds the sandwiched dye layer in a rigid structure which facilitates attachment to and detachment from a sensor probe while protecting the dye layer.
Therefore, it is an object of the present invention to provide a sensor capsule for facilitating mounting of an indicator element to a sensor probe.
It is a further object of the invention to provide a sensor capsule which includes sandwiched layers for retaining a dye solution.
It is yet another object of the invention to provide a sensor capsule which provides a rigid housing for enclosing a sandwiched dye layer.
Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.